A combine is a machine that is used in grain farming to harvest a variety of crops from a field. Combines are typically self-propelled, but some are also towed and powered by tractors. As a combine moves through a field during a harvesting operation, the ripened crop is cut from the field by a header at the front of the combine. The crop is then transferred into threshing and separating assemblies within the combine, where grain is removed from the crop material. The grain is separated from the chaff and brought to a hopper in the combine, or off-loaded to a truck or other storage mechanism. The residual crop material remaining after the grain has been removed is expelled from the rear of the combine, or chopped into smaller elements and then expelled from the rear of the combine. When harvesting, it is desirable that the crop residue be expelled along a path that is approximately the same width as the width of the crop that is cut by the header. This can be done with a variety of different types of chopping and spreading mechanisms. However, as the width of the cutting head has increased, there has been a need for spreading mechanisms that can achieve a spread width for the residual crop material that matches the width of the header and spreads the residual crop material generally evenly across that path width.
Some devices simply spread the material behind the machines; other chop the material into more evenly sized elements before spreading the material so as to achieve a more uniform distribution. Many devices, such as those disclosed in U.S. Pat. No. 6,251,009 to Grywacheski and U.S. Pat. No. 6,331,142 to Bischoff et al, incorporate a straw chopper and utilize a distributing device that has a series of guide vanes to disperse the residual crop material across a broader area. However, these types of systems do not work as well with very wide headers, as uniform distribution across the wider cutting path cannot be achieved using devices such as this. U.S. Pat. No. 5,082,186 to Bruns discloses a pair of rotating straw and chaff spreaders positioned behind the harvester. However, this device is directed to combines in which the straw and chaff are distributed in separate streams. In many modern combines, the straw and chaff are combined inside the combine and both processed through the straw spreader to provide a more uniform mixture of residual crop material to be distributed. U.S. Pat. No. 6,070,816 to Hirsch discloses a straw chopper comprised of two shaft-driven rotors that incorporate chopping blades into the housing of the rotor such that rotating crop material is chopped as it is rotated around on the rotors and comes in contact with the blades mounted around the inside of the housing. The material is rotated around the housing on the rotors, being chopped and then dispelled out behind the combine. However, it has been found that this mechanism, while an efficient utilization of space, cannot achieve a wide-spread distribution of crop material, owing to the necessity of chopping the material while it is being rotated inside of the chopper, and then deposited behind the machine.
Devices that utilize both a chopper mechanism and a separate impeller-type spreader attached aft of the chopper have been found to be more efficient in providing uniform spreading of crop material behind a combine in a wider path. A chopper and impeller-type spreader is an assembly attached to the rear of the combine that is adapted to receive crop residue expelled from the combine, process it through the chopper, cutting it into smaller pieces if necessary, and evenly broadcasting the residual crop material over a wide area of ground behind the combine. U.S. Pat. No. 5,215,500 to Kirby discloses a mechanism having an impeller-type spreader that receives straw and chaff crop residue material from the combine and spreads it behind the combine. However, this invention utilizes a single rotating impeller behind the combine. Such a mechanism provides only a limited width of spread behind the combine, and cannot achieve a sufficient width of spread to match the width of current cutting headers, thus resulting in an uneven spread of crop material behind the combine when the combine is used with modern wide-width cutting headers.
An impeller-type spreader typically comprises a right-side impeller and a left-side impeller that counter-rotate on parallel axes. Generally, distribution of crop residue from the right-side of the combine is attributed to the right-side impeller, and similarly, distribution of crop residue from the left-side of the combine is attributed to the left-side impeller. The overall width of crop residue distribution by the spreader is largely dependent on the rotational speed of the impellers. The higher the rotational speed of the impellers, the wider the resulting broadcast width. A number of chopper and impeller-type spreaders are known in the industry. For example, U.S. Pat. No. 6,238,286 to Aubry, et al., U.S. Pat. No. 6,416,405 to Niermann and U.S. Pat. No. 6,663,485 to Niermann all disclose systems in which crop residue material is routed from the chopper into a dual impeller-type spreader that is located below or in the same plane as the chopper. Such mechanisms work fairly efficiently. However, a mechanism that could better utilize the momentum of the residual crop material that is being dispersed from the chopper would achieve an improved area of dispersion of crop material behind the combine, which could more easily cover the entire width of the cutting header path.
When crop residue is broadcast by a spreader, it is desirable that the residue be spread evenly across the area that has just been harvested. Even distribution of crop residue ensures that the residue deteriorates and covers the field consistently, providing for uniform working of the ground, fertilization and crop emergence for the next year's crops. As the harvesting devices affixed to the front of a combine become wider and wider, it is more difficult to achieve an even distribution of crop residue across the entire width of the harvested rows. This is particularly true where the crop residue is very fine, very heavy, or moist. In some instances, spreaders of the current art can become clogged or not provide proper flow, and will produce an inconsistent crop residue spread. Thus an effective means of maintaining a constant wide spreader broadcast width and location, regardless of external or crop conditions, is desired.